This invention relates generally to an image storage and retrieval apparatus and more particularly relates to an apparatus for storing more than 2000 still color video images on a storage medium, such as a magnetic disk, and retrieving the images for display and processing.
Current digital recording with its attendant cost has prevented high density storage of still color video images and high speed random access with erasability. The problem with storage of color images in digital form is the tremendous amount of storage capacity required, typically 500+ kilobytes of storage per image. Optical discs, while providing high density storage, are not erasable at reasonable costs.
In video recording, the luminance and color components of a video signal are either recorded together on a single magnetic track or are recorded separately on two or more tracks. Predictably, there are advantages and drawbacks to each approach. Single track recording requires less recording media space and thereby increases the number of images that can be placed on a given magnetic media. Recording the video signal components on two or more tracks usually improves the image quality, but severely complicates the apparatus and reduces the storage capacity of a given media by one half or more.
Early video disk recorders for replays were pioneered by Ampex and others in the 1960's and used both rigid and floppy disk magnetic media for storage of images. These systems typically used a narrow band FM recording of the modulated analog signal and stored a single video frame with each rotation of the disk. Although providing the user with some excellent advantages, such as a high image storage density and quick access times, these units were sufficiently expensive to limit their use to high priced systems in broadcasting and medical imaging. Further, these early units were limited by the irregularities in and on the surface of the recording media. This led researchers at that time to discover that frequency modulation, versus amplitude modulation, was a more effective way to encode the video signal. These systems also required a high head-to-media relative velocity of 1,000 to 2,000 inches per second, due to head gap lengths, short video wave lengths required, and high signal-to-noise requirements. In the floppy disk versions of these systems where the heads were in constant contact with the media, the useful life was limited, usually less than 1,000 hours. In the rigid disk versions, useful life might approach 2,500 hours --prolonged by the air space between the heads and media, but limited due to manufacturing imperfections, wear from occasional head-to-media contact, and other factors.
Image storage technology today is characterized by the movement from film and slides to videotape and video disk to digitized images in digital mass storage. This recent technology has taken two directions: the first is a trend toward digital video disk or CD-ROM (Compact Disk-Read Only Memory); the second, a trend toward WORM (Write Once, Read Many) storage. Both of these technologies have significant drawbacks in that they are not erasable and suffer from high media storage capacity requirements. The market today has seen the introduction of lower cost, high quality digitized storage of images. However, the problem as previously noted with storage of color images in digital form is that it takes a tremendous amount of information storage capacity, typically 500+ kilobytes of storage per image.
The need for a compact, inexpensive, totally self-contained image recorder, storage unit, playback and monitoring device for storing large numbers of high quality still color images is apparent in several fields: security and surveillance, entry access systems, computer peripherals, training devices, and picture archiving systems, and as a replacement for color slide projectors, to name only a few.